This invention references commonly assigned U.S. Pat. Nos. 5,910,041; 5,967,882; 5,993,298; 6,048,254; 6,102,777; 6,120,352; 6,149,506; 6,607,157; 6,752,700; 6,769,969; 7,632,434 and 7,520,800 and commonly assigned U.S. patent application published numbers 20100003904, 20080299875 and 20050118939 and all contents of which are incorporated herein by reference.
U.S. Pat. No. 7,614,939 (Tolles et al) describes a CMP polishing machine that uses flexible pads where a conditioner device is used to maintain the abrading characteristic of the pad. Multiple CMP pad stations are used where each station has different sized abrasive particles. U.S. Pat. No. 4,593,495 (Kawakami et al) describes an abrading apparatus that uses planetary workholders. U.S. Pat. No. 4,918,870 (Torbert et al) describes a CMP wafer polishing apparatus where wafers are attached to wafer carriers using vacuum, wax and surface tension using wafer. U.S. Pat. No. 5,205,082 (Shendon et al) describes a CMP wafer polishing apparatus that uses a floating retainer ring. U.S. Pat. No. 6,506,105 (Kajiwara et al) describes a CMP wafer polishing apparatus that uses a CMP with a separate retaining ring and wafer pressure control to minimize over-polishing of wafer peripheral edges. U.S. Pat. No. 6,371,838 (Holzapfel) describes a CMP wafer polishing apparatus that has multiple wafer heads and pad conditioners where the wafers contact a pad attached to a rotating platen. U.S. Pat. No. 6,398,906 (Kobayashi et al) describes a wafer transfer and wafer polishing apparatus. U.S. Pat. No. 7,357,699 (Togawa et al) describes a wafer holding and polishing apparatus and where excessive rounding and polishing of the peripheral edge of wafers occurs. U.S. Pat. No. 7,276,446 (Robinson et al) describes a web-type fixed-abrasive CMP wafer polishing apparatus.
U.S. Pat. No. 6,786,810 (Muilenberg et al) describes a web-type fixed-abrasive CMP article. U.S. Pat. No. 5,014,486 (Ravipati et al) and U.S. Pat. No. 5,863,306 (Wei et al) describe a web-type fixed-abrasive article having shallow-islands of abrasive coated on a web backing using a rotogravure roll to deposit the abrasive islands on the web backing. U.S. Pat. No. 5,314,513 (Milleret al) describes the use of ceria for abrading.
Various abrading machines and abrading processes are described in U.S. Pat. Nos. 5,364,655 (Nakamura et al). 5,569,062 (Karlsrud), 5,643,067 (Katsuoka et al), 5,769,697 (Nisho), 5,800,254 (Motley et al), 5,916,009 (Izumi et al), 5,964,651 (hose), 5,975,997 (Minami, 5,989,104 (Kim et al), 6,089,959 (Nagahashi, 6,165,056 (Hayashi et al), 6,168,506 (McJunken), 6,217,433 (Herrman et al), 6,439,965 (Ichino), 6,893,332 (Castor), 6,896,584 (Perlov et al), 6,899,603 (Homma et al), 6,935,013 (Markevitch et al), 7,001,251 (Doan et al), 7,008,303 (White et al), 7,014,535 (Custer et al), 7,029,380 (Horiguchi et al), 7,033,251 (Elledge), 7,044,838 (Maloney et al), 7,125,313 (Zelenski et al), 7,144,304 (Moore), 7,147,541 (Nagayama et al), 7,166,016 (Chen), 7,250,368 (Kida et al), 7,367,867 (Boller), 7,393,790 (Britt et al), 7,422,634 (Powell et al), 7,446,018 (Brogan et al), 7,456,106 (Koyata et al), 7,470,169 (Taniguchi et al), 7,491,342 (Kamiyama et al), 7,507,148 (Kitahashi et al), 7,527,722 (Sharan) and 7,582,221 (Netsu et al).
I. Double-Sided Abrading
To produce parallel-surfaced workpieces, a different machine technology is used. Here, a large-diameter rigid precision-flat rotating platen is provided. Multiple equal-thickness workpieces are positioned around the circumference of the platen. Then, another large diameter flat-surfaced abrading platen is placed in contact with the top surfaces of the multiple workpieces. Here, the upper platen is allowed to float spherically so its flat surface assumes parallelism with the surface of the bottom platen. Both the upper and bottom platens have equal-diameter abrading surfaces. With this technology, no attempt is made to rigidly position the surface of the upper moving abrasive platen surface precisely perpendicular to the surface of the bottom platen. This co-planar alignment of the two double-sided abrading platens is achieved with ease and simplicity by using the uniform-thickness workpieces as spacers between the two [platens.
II. Raised-Island High Speed Flat Lapping
All of the present precision-flat abrading processes have very slow abrading speeds of about 5 mph. The high speed flat lapping system can operate at speeds of approximately 100 mph. Increasing abrading speeds increase the material removal rates. This results in high workpiece production and large cost savings. In addition, those abrading processes that use liquid abrasive slurries are very messy. The fixed-abrasive used in high speed flat lapping eliminates the slurry mess. Another advantage is the quick-change features of the high speed lapper system where abrasive disks can be quickly changed with use of the disk vacuum attachment system. Changing the sized of the abrasive particles on all of the other abrading systems is slow and troublesome.
III. Quick-Change Abrasive Disks
Vacuum is used to quickly attach flexible abrasive disks, having different sized particles, different abrasive materials and different array patterns and styles of raised islands. Each flexible disk conforms to the precision-flat platen surface provide precision-flat planar abrading surfaces. Quick lapping process set-up changes can be made to process a wide variety of workpieces having different materials and shapes with application-selected raised island abrasive disks that are optimized for them individually. Small and medium diameter disks can be stored or shipped flat in layers. Large and very large disks can be rolled and stored or shipped in polymer protective tubes. The abrasive disk quick change capability is especially desirable for laboratory lapping machines but they are also great for prototype lapping and full-scale production lapping machines. This abrasive disk quick-change capability also provides a large advantage over micro-grinding where it is necessary to change-out a worn heavy rigid platen or to replace it with one having different sized particles.
IV. Hydroplaning of Workpieces
Hydroplaning of workpieces occurs when smooth surfaces (continuous thin-coated abrasive) are in fast-moving contact with a flat surface in the presence of surface water. However, it does not occur when interrupted-surfaces (raised islands) contact a flat wetted workpiece surface. An analogy is the tread lugs on auto tires which are used on rain slicked roads. Tires with lugs grip the road at high speeds while bald smooth-surfaced tires hydroplane.
V. Maintaining Abrasive Disk Flat Surface
Care is taken during the lapping procedures to maintain the precision flatness of the abrasive surface. This is done by selecting abrasive disks where the full surface of the abrasive is contacted by the workpiece surface. This results in uniform wear-down of the abrasive. Other techniques can also be used to accomplish this. First, a workpiece that is smaller than the radial width of the annular band of abrasive islands can be oscillated radially during the abrading procedure to overlap both the inner and outer edges of the annular abrasive band. This prevents the formation of tangential raised ribs of abrasive inboard and outboard of the wear-track of the workpiece.
Also, stationary-position conditioning rings can be used in flat contact with the moving abrasive. These rings have diameters that are larger than the radial width of the abrasive island annular band. They preferentially remove the undesirable raised abrasive high spot areas or even raised rib-walls of abrasive that extend around the circumference of the annular band of abrasive. The conditioning rings are similar to those used in slurry lapping to continually maintain the flatness of the rotating slurry platen.
Many of the different techniques used here to maintain the flatness of annular band of fixed-abrasive coated raised islands during the abrading life of an abrasive disk are highly developed and in common use in slurry lapping. In slurry lapping, a liquid mixture that contains loose abrasive particles continuously wears recessed circumferential tracks in the rigid metal platen surface. However, unlike slurry lapping, there is no abrasive wear of the high speed flat lapper platens because only the flexible disk backing contacts the platen surface. Here, the precision flatness of the high speed flat lapper system is re-established by simply changing the abrasive disk.
Because the upper platen uses a spherical bearing that allows the platen to float, the platen holding mechanism can be a simple pivot arm device. The platen spherical-action bearing provides radial support for the platen during rotation so the platen retains its balance even when it is operated at great speeds. Conformal flat contact of the two platens prevents wobble of the upper platen as it is rotated. It is not necessary that the pivot arm position the upper platen in a precision concentric alignment with the lower platen during a double-sided lapping operation.
VI. Raised Island Disks
The reason that this lapping system can be operated at such high speeds is due to the use of precision-thickness abrasive coated raised island disks. Moving abrasive disks are surface cooled with water to prevent overheating of both the workpiece and the abrasive particles. Raised islands prevent hydroplaning of the stationary workpieces that are in flat conformal contact with water wetted abrasive that moves at very high speeds. Abrading speeds are often in excess of 100 mph. Hydroplaning occurs with conventional non-island continuous-coated lapping film disks where a high pressure water film is developed in the gap between the flat workpiece and the flat abrasive surfaces.
During hydroplaning, the workpiece is pushed up away from the abrasive by the high pressure water and also, the workpiece is tilted. These cause undesirable non-flat workpiece surfaces. The non-flat workpieces are typically polished smooth because of the small size of the abrasive particles. However, flat-lapped workpieces require surfaces that are both precision-flat and smoothly polished.
The islands have an analogy in the tread lugs on auto tires which are used on rain slicked roads. Tires with lugs grip the road at high speeds while bald tires hydroplane. Conventional continuous-coated lapping film disks are analogous to the bald tires.
Raised islands also reduce “stiction” forces that tend to bond a flat surfaced workpiece to a water wetted flat-surfaced abrasive surface. High stiction forces require that large forces are applied to a workpiece when the contacting abrasive moves at great speeds relative to the stationary workpiece. These stiction forces tend to tilt the workpiece, resulting in non-flat workpiece surfaces. A direct analogy is the large attachment forces that exist between two water-wetted flat plates that are in conformal contact with each other. It is difficult to slide one plate relative to the other. Also, it is difficult to “pry” one plate away from the other. Raised island have recessed channel passageways between the island structures. The continuous film of coolant water that is attached to the workpiece is broken up by these island passageways. Breaking up the continuous water film substantially reduces the stiction.
VII. Precision Thickness Disks
Another reason that this lapping system can be operated at such high speeds is due to the use of precision-thickness abrasive coated raised island disks. These disks have an array of raised islands arranged in an annular band on a disk backing. The top flat surfaces of the islands are coated with a very thin coating of abrasive. The abrasive coating consists of a monolayer of 0.002 inch beads that typically contain very small 3 micron (0.0001 inch) or sub-micron diamond abrasive particles. Raised island abrasive disks are attached with vacuum to ultra-flat platens that rotate at very high abrading surface speeds, often in excess of 100 mph.
The abrasive disks have to be of a uniform thickness over the full abrading surface of the disk for three primary reasons. The first reason is to present all of the disk abrasive in flat abrading contact with the flat workpiece surface. This is necessary to provide uniform abrading action over the full surface of the workpiece. If only localized “high spots” abrasive surfaces contact a workpiece, undesirable tracks or gouges will be abraded into the workpiece surface. The second reason is to allow all of the expensive diamond abrasive particles contained in the beads to be fully utilized. Again if only localized “high spots” abrasive surfaces contact a workpiece, those abrasive particles located in “low spots” will not contact the workpiece surface. Those abrasive beads that do not have abrading contact with a workpiece will not be utilized. Because the typical flatness of a lapped workpiece are measured in millionths of an inch, the allowable thickness variation of an raised island abrasive disk to provide uniform abrasive contact must also have extra-ordinary accuracy.
The third reason is to prevent fast moving uneven “high spot” abrasive surfaces from providing vibration excitation of the workpiece that “bump” the workpiece up and away from contact with the flat abrasive surface. Because the abrasive disks rotate at such high speeds and the workpieces are lightweight, these moving bumps tend to repetitively drive the workpiece up after which it falls down again with only occasional contact with the moving abrasive. The result is uneven wear of the workpiece surface.
All three of these reasons are unique to high speed flat lapping. The abrading problems, and solutions described here were progressively originated while developing this total lapping system. They were not known or addressed by others who had developed raised island abrasive disks. Because of that, their disks can not be used for high speed flat lapping.
VIII. Configurations of Workholder Machines
The wire-driven workholder abrading machines can have a variety of configurations. Wire-driven workholders can be used for single-sided abrading or for double-sided abrading. For single-sided abrading, the rotary workholders are positioned where the workpieces that are contained by the workholders are held in flat-surfaced contact with an abrasive coated flat-surfaced rotating platen. For double-sided abrading, the rotary workholders are positioned where the workpieces that are contained by the workholders are positioned between an upper abrasive coated rotary platen and a lower abrasive coated rotary platen. Here, the upper abrading rotary platen can be a floating platen or the upper abrading rotary platen can be rigidly mounted.
Single wire-driven workholders can be used or multiple wire-driven workholders can be used for single-sided abrading and for double-sided abrading. When floating upper platens are used, at least three workholders that evenly-spaced from each other are used to provide stable three-point support of the floating upper platen that is abrading contact with the workpieces that are supported by the lower platen.
The workholder flexible drive-wires can be formed from a long length of a flexible wire that can be used to rotate the workholder disks. Or, continuous-loops of wire can be used to drive one or more of the workholder disks. Continuous-loops of wire can be used for each individual workholder disk or continuous-loop wires can be used to drive multiple workholder disks. Flexible drive wires are guided in grooves in the outer periphery of the workholder disks and also, in the peripheries of other wire-guiding devices. The flexible drive-wires are driven by drive motors and wire-tensioning devices provide wire tension on the flexible drive-wires. The flexible drive wires can be fabricated from a wide variety of metal, polymer or organic materials and they can be end-joined together to form woven, fused, welded, or adhesively-bonded butt-joints for fabrication of continuous-loop drive-wires.
The workholders can be translated or rotated away from the lower platens to provide access for changing the abrasive coating on the lower platen and also, on the upper platens.
In addition, special workholder disk support devices can be used to support the workholder disks where the workholder disks do not contact the abrasive surface of the lower abrading platen or the workholder disks do not contact the abrasive surface of the upper abrading platen. Here, a rotatable workholder support disk can be attached to the rotatable lower platen with a rotatable bearing. It is in rolling contact with the workholder disk or disks and the rotatable workholder support disk can engage the workholder disks and restrain the workholder disks in a direction that is perpendicular to the surfaces of the workholder disks. Use of the rotatable workholder support disk along with workholder disk support idlers can provide support of the workholder disks where there is a controlled gap between the workholder disk flat surfaces and the lower and upper rotary platens flat abrasive surfaces. The rotatable workholder support disk can also engage the workholder disks and restrain the workholder disks in a radial direction relative to workholder disks' diameters.
IX. Types of Abrading with Wire-Driven Workholders
A wide variety of types of lapping, polishing or abrading flat-surfaced workpieces can be accomplished using the wire-driven workholder abrading machines. Wire-driven workholders can be used for single-sided abrading where only one surface of a workpieces is abraded or they can be used double-sided abrading where both opposed surfaces of a workpieces are simultaneously abraded. In one machine configuration, either/or both the upper rotatable platen and the lower rotatable abrading platen approximately horizontal flat annular abrading-surface can have a variety of abrasive coatings. These abrading platens can also have vertical or angled flat annular abrading-surfaces.
Abrasive coatings on the platens surfaces that can be provided can be selected from the group consisting of flexible abrasive disks, flexible raised-island abrasive disks, flexible abrasive disks with resilient backing layers, flexible abrasive disks with resilient backing layers having a vacuum-seal polymer backing layer, flexible abrasive disks having attached solid abrasive pellets, flexible chemical mechanical planarization (CMP) resilient disk pads that are suitable for use with liquid abrasive slurries, flexible chemical mechanical planarization resilient disk pads having nap covers, flexible shallow-island chemical mechanical planarization abrasive disks, flexible shallow-island abrasive disks with resilient backing layers having a vacuum-seal polymer backing layer, flexible flat-surfaced metal or polymer disks, and liquid abrasive-slurry coatings.